Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards

Heat and the Second Law of Thermodynamics

Heat, the Transfer of Thermal Energy, and the Second Law of Thermodynamics

NSES Generalization (p. 180)

Everything tends to become less organized and less orderly over time. Thus, in all energy transfers, the overall effect is that the energy is spread out uniformly. Examples are the transfer of energy from hotter to cooler objects by conduction, radiation, or convection, and the warming of our surroundings when we burn fuels.

Further Description:

This is an overgeneralization that is quite unclear. Everything does not tend to disorder over time. One subsystem can produce order in another subsystem over time, making the one more disordered while the other is ordered. This is what happens in photosynthesis, when glucose is synthesized (atoms made more ordered). The energy entering the system increases the order of the particles in the leaf. What is important is the overall effect.

It is the closed system, in which particles interact and into and out of which no energy or mass can enter or leave, that must become more disordered over time. This aspect of energy provides the theoretical framework to explain empirical laws of heat transfer and their connections to mechanical work done in a cycle. This leads to thermodynamic efficiency and the second law of thermodynamics. Applications include heat engines. The entropy aspects of the second law also need to be considered. The impossibility of perpetual motion machines of the first kind and especially of the second kind can now be examined.

Concepts Needed:

Grade 9

Temperature, heat, conduction, convection, radiation, insulation, phase change, gas, solid, liquid, freezing point, boiling point, calorie, calorimeter

Grade 10

Absorption, reflection, vapor, specific heat, calorimetry, mechanical equivalent of heat

Grade 11

Heat of fusion, heat of vaporization

Grade 12

Efficiency (thermodynamics), coefficient of performance, order, disorder, entropy

Empirical Laws or Observed Relationships:

Heat added = mass times specific heat times temperature change; Newton=s law of cooling; Wien=s displacement law; Charles= law (to establish the need for absolute temperature); absolute temperature

Theories or Models:

Stefan-Boltzmann fourth power radiation law, thermodynamics, the Carnot cycle, the entropy of systems

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Micro-Unit Description:

Heat and the Second Law of Thermodynamics
At this level, students should be able to measure temperatures, know the definition of the calorie, do simple calorimetry experiments, and make other simple measurements associated with heat transfer. The concepts of radiation, convection, and conduction should be understood in qualitative ways.Even though students will have learned the definition of work and are able to calculate work done in units of joules, they should not convert calories to joules at this level. (The practice of using joules for heat obscures the fundamental discoveries of the relationship between work and heat, beginning with the qualitative observations of Rumford in drilling cannon and culminating with the quantitative measurements by Joule. This fundamental and important relationship is lost from most science textbooks as a consequence of the compulsion of writers and publishers to use SI units exclusively.)Students should understand chemical energy and changes in matter. They should be able to determine the caloric value of an energy source (like sugar).

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